# Pay-per-call payment protocols for AI agents (slim)

> 3 pay-per-call protocols ranked by the Anchor benchmark. Leader Machine Payments Protocol (MPP) (A). Protocols where an API answers with a payment request, the agent pays and retries the call. x402, MPP and L402 compared on who governs them, what rails and assets they settle on, what a payment costs, how long settlement takes and what security researchers have found.

- Full: https://www.anchorterminal.com/categories/pay-per-call.md (~1,100 tokens) · this version ~280 tokens · JSON https://www.anchorterminal.com/categories/pay-per-call.json · canonical https://www.anchorterminal.com/categories/pay-per-call
- Index: https://www.anchorterminal.com/llms.txt · API: https://www.anchorterminal.com/api/v1/index.json · Updated: 2026-10-04

- Tools: 3 · agent-ready (BB+): 2 · accept x402: 0 · JSON: https://www.anchorterminal.com/api/v1/tools.json · by capability: https://www.anchorterminal.com/api/v1/capabilities.json
- Capabilities: payments.protocol, payments.x402, payments.stablecoin, payments.lightning

| # | Tool | Grade | Score | Confidence | x402 | Auth | Where | Slim |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| not ranked, protocol | Machine Payments Protocol (MPP) | A | 81.1 | medium | no | None | spec | https://www.anchorterminal.com/tools/mpp.min.md |
| not ranked, protocol | x402 | A | 79.7 | high | no | None | spec | https://www.anchorterminal.com/tools/x402.min.md |
| not ranked, protocol | L402 | C | 60.5 | medium | no | None | spec | https://www.anchorterminal.com/tools/l402.min.md |